Fiber ringdown pressure/force sensors

• US 7,241,986 B2
• Filed: 10/08/2004
• Issued: 07/10/2007
• Est. Priority Date: 10/08/2003
• Status: Expired due to Fees

• Current Assignee: Mississippi State University
• Original Assignee: Mississippi State University
• Inventors: Wang, Chuji
• Primary Examiner(s): Luu; Thanh X.
• Assistant Examiner(s): ELLIS, SUEZU Y
• Application Number:
  US10/960,075
• Publication Number:
  US 20050103988A1
• Time in Patent Office: 1,005 Days
• Field of Search: 25022714-22718, 250/231.19, 385 12- 14, 385/42, 385/15, 356/73.1, 356/32
• US Class Current: 250/227.14
• CPC Class Codes: G01L 1/243 using means for applying force perpendicular to the fibre axis

Abstract

A novel fiber ringdown (FRP) pressure sensor is provided for measuring extremely high pressures under extreme environmental conditions of cold and heat. Pressure measurements are achieved in a time domain by measuring ringdown times of emitted light through the fiber optic loop of the device. The novel FRP sensor can include a light source, such as a diode laser light source, two 2×1 fiber couplers, a section of fused silica single mode fiber, a photodetector, and an electronic control. The novel FRP sensor'"'"'s performance in the areas of stability, reproducibility, dynamic range, and temperature tolerance are far above those of conventional sensors.

Claims

1. A sensing device comprising:

a laser light source for producing a laser beam;

a control component connected to said laser light source for controlling activation or deactivation of said laser light source;

at least one section of optical fiber, configured to receive at least a portion of said laser beam and transmit at least a portion of said received laser beam within said optical fiber;

at least one fiber coupler, wherein said at least one fiber coupler and said at least one section of optical fiber are spliced together to form a fiber loop;

at least one sensor component, said sensor component configured to induce a loss in light from said optical fiber as a function of pressure exerted on the sensor component; and

a photodetector, said photodetector configured to receive a signal originated from said sensor component and transmitted to said photodetector via said fiber coupler;

wherein said signal provides data, wherein said data is analyzed and processed to determine a ringdown time in said fiber loop and wherein said determined ringdown time is used to determine a pressure being applied on the sensor component; and

wherein said ringdown time (τ

) is related to the force applied by the following equation;

$\mathrm{\tau <br><br>}={\mathrm{\tau <br><br>}}_0<br><br>\left(1-\frac{\mathrm{\beta <br><br>}<br><br><br><br>l}{\mathrm{\alpha <br><br>}<br><br><br><br>L+E}<br><br>F\right)$

where τ

₀ is a ringdown time when no force is applied, F is the force applied, α

is the wavelength dependent absorption coefficient for fiber core material of said optical fiber, β

is the force induced loss coefficient, l is the length of a fiber portion that has direct contact with the force being applied, L is the total length of said optical fiber, and E is total insertion losses of said fiber couplers.

2. The device of claim 1, further comprising a data acquisition system functionally connected to said photodetector for the acquisition of data sent from said photodetector.

3. The device of claim 2, wherein said data acquisition system analyzes and processes said data.

4. The device of claim 1, wherein said laser light source is a diode laser light source.

5. The device of claim 4, wherein said diode laser light source is selected from the group consisting of a temperature controlled diode laser, an external cavity diode laser, and a combination of multiple laser diodes used together to serve as a broad band tunable laser light source.

6. The device of claim 1, wherein said laser light source produces a laser beam having a wavelength from ultraviolet to near infrared in a range of 300 nm-10 μ

m.

7. The device of claim 1, wherein said laser light source produces a laser beam having a wavelength of about 1650 nm.

8. The device of claim 1, wherein said control component is an electrical control, said electrical control utilizing a pulsed wave generator.

9. The device of claim 1, wherein said control component is an electrical control, said electrical control utilizing a continuous wave generator.

10. The device of claim 1, wherein said control component is an electrical control, said electrical control utilizing an electrical board to achieve control.

11. The device of claim 1, wherein said at least one fiber coupler comprises a 2×

1 fiber coupler.

12. The device of claim 1, wherein said device comprises multiple sensor heads, each of said multiple sensor heads being adapted to sense pressure, temperature or species in said same device.

13. The device of claim 1, wherein said device comprises a single fiber loop for measuring a single parameter.

14. The device of claim 1, wherein said device comprises multiple fiber loops for measuring multiple parameters in said device, said multiple parameters being more than one member selected from the group consisting of pressure, temperature, and species.

15. The device of claim 1, wherein said sensor component comprises a loading platform, said loading platform comprising a plate positioned on top of said sensor component.

16. The device of claim 1, wherein said sensor component is the location where force is applied when said device is sensing pressure.

17. The device of claim 1, wherein said sensing device senses pressure in the range of 0-150,000 psi.

18. The device of claim 1, wherein said pressure sensing is effective at temperatures ranging between 77-1900K.

19. The device of claim 1, wherein a fiber jacket encloses said section of optical fiber and said jacket is removed from said sensor head so as to increase sensitivity of said sensor head.

20. The device of claim 1, further comprising an optical component for increasing sensitivity of said device.

21. The device of claim 20, wherein said optical component is a fiber Bragg grating.

22. A method of sensing pressure, the method comprising:

(a) providing a pressure sensing device, said pressure sensing device comprising;

a laser light source for producing a laser beam;

a control component connected to said laser light source for controlling activation and deactivation of said laser light source;

at least one section of optical fiber oriented in a ringdown configuration and oriented to said light source so as to receive at least a portion of said laser beam and transmit at least a portion of said received laser beam within said optical fiber;

at least one fiber coupler;

at least one sensor component, said sensor component configured to induce a loss in light from said optical fiber as a function of pressure exerted on the sensor component;

a photodetector, said photodetector configured to receive a signal originated from said sensor component and transmitted to said photodetector via said fiber coupler; and

a data acquisition system functionally connected to said photodetector to receive data sent from said photodetector;

(b) activating said control component to control emission of light from said light source such that a portion of light emitted from said light source upon activation is transmitted through said at least one section of optical fiber, said control component acting to deactivate emission of light from said light source such that light initially emitted rings inside said at least one section of optical fiber for the course of said ringdown configuration, and at each round trip of said emitted light in said ringdown configuration, said emitted light loses a fraction of leaked light as it leaks from said at least one section of optical fiber and is transferred to said photodetector via said fiber coupler and a remnant of emitted light continuing to ring down in said optical fiber;

(c) determining a first ringdown time for said emitted light and a second ringdown time for a second emitted light that rings down when pressure is exerted on sensor component;

(d) determining a pressure exerted on said sensor component by comparing said first ringdown time and second ringdown time, wherein said second ringdown time (τ

) is related to a force applied by the following equation;

$\mathrm{\tau <br><br>}={\mathrm{\tau <br><br>}}_0<br><br>\left(1-\frac{\mathrm{\beta <br><br>}<br><br><br><br>l}{\mathrm{\alpha <br><br>}<br><br><br><br>L+E}<br><br>F\right)$

where τ

₀ is the first ringdown time when no force is applied, F is the force applied, α

is the wavelength dependent absorption coefficient for fiber core material of said optical fiber, β

is the force induced loss coefficient, l is the length of a fiber portion that has direct contact with the force being applied, L is the total length of said optical fiber, and E is total insertion losses of said fiber couplers, and

(e) outputting a result of step (d).

23. The method of claim 22, wherein said sensing device senses pressure in the range of 0-150,000 psi.

24. The method of claim 22, wherein said pressure sensing device is provided with a vacuum system for forming a low atmospheric pressure environment around said sensor component, whereby said sensor component can sense negative pressure.

25. The method of claim 22, wherein said pressure sensing is effective at temperatures ranging between 77-1900K.

26. The method of claim 22, wherein said activation and deactivation of said laser light source is at a frequency in the range of 1 Hz to 1 MHz.

27. The method of claim 26, wherein said frequency is about 10 Hz.

28. The method of claim 22, wherein said pressure sensing is not effected by electromagnetic interference.